The present invention relates generally to positioning items of equipment within a subterranean well and, in an embodiment described herein, more particularly provides a locating and locking mandrel system.
When positioning an item of equipment, such as a wireline-conveyed subsurface safety valve, within a tubing string installed in a subterranean well, it is common practice to attach a lock mandrel to the valve and then convey the valve and lock mandrel into the string. The lock mandrel is then operatively engaged with a nipple interconnected in the string. Typically, the engagement between the mandrel and the nipple anchors the valve in position in the string and seals the valve to the string, so that flow through the string is constrained to pass through the valve.
When initially positioned in the nipple, it is typical for the weight of the valve to be supported by a no-go member of the mandrel. The no-go member may be a cylindrical member or ring having an outer diameter somewhat greater than an inner no-go diameter of the nipple. In this manner, engagement between the no-go member and the no-go diameter prevents the mandrel from passing through the nipple and thereby supports the weight of the valve on the no-go diameter. After the no-go member has engaged the no-go diameter, a locking member, such as a radially extendable dog or lug, is engaged with an internal profile of the nipple, in order to lock or anchor the mandrel in position relative to the nipple.
However, it has become increasingly prevalent to utilize large diameter tubing strings with large seal bores in wells, in order to maximize fluid flow therethrough. In designing tools for use in such large diameter tubing strings, the tool designer is faced with several problems. Larger diameter tools tend to have increased weight and, thus, in the typical lock mandrel and nipple system, increased weight must be borne by the no-go diameter of the nipple when engaged by the no-go member. Additionally, in order to provide a larger bore, the wall thickness of the nipple may be decreased, so that only a small area is available to support the weight of the valve.
Furthermore, lock mandrels and nipples have in the past required that a radially outwardly extending or biased locating and/or locking member of the mandrel, such as the lugs or dogs mentioned above, pass through a seal bore of the nipple before a seal of the mandrel sealingly engages the seal bore. It will be readily appreciated that this situation may cause damage to the seal bore by the locating and/or locking member, so that the seal cannot effectively engage the seal bore.
From the foregoing, it may be seen that it would be highly advantageous to provide a locating and locking mandrel system which is specially adapted for use in situations in which it is undesirable to support the weight of an item of equipment on a no-go diameter of a nipple. Additionally, it would be advantageous to provide a locating and locking mandrel system in which a seal surface of a nipple is protected from damage due to contact with a locating and/or locking member of the mandrel.